1. Technical Field
The present invention—involving bookbinding units that form encased booklets by binding into coversheets inner-leaf sheets that have been collated into bundles—relates to improvements in cover-binding mechanisms for securely binding into booklets inner-leaf sheets having single leaves mixed with saddle-stitch folded sheets.
2. Description of the Related Art
Bookbinding units that in general collate into bundles sheets that have been printed in a digital printer or other printing machine and encase the bundles in coversheets to form booklets are widely known. With this scheme, inner-leaf sheets collated into a sheet bundle are set into a stack on an inner-leaf tray, and the bundled sheets are conveyed from the tray to an adhesive-application location, and an adhesive (such as a hot-melt adhesive) is applied to a spine-portion endface of the sheets. Meanwhile, a coversheet from a coversheet tray is fed to, and set into place at, a cover-binding location arranged downstream of the adhesive-application location; the spine portion of the inner-leaf sheets, where the adhesive has been applied, is joined to a cover-binding portion of the coversheet in its middle; and thereafter the coversheet is spine-creased and molded in a coversheet pressing means.
Conventionally, as disclosed in Japanese Unexamined Pat. App. Pub. No. 2003-025759, an inner-leaf tray is disposed on one end of the unit, and a cover tray is disposed on the other end. The inner-leaf tray stores collated and stacked inner-leaf sheets (bundles), and the coversheet tray stores a plurality of coversheets of predetermined sizes. The inner-leaf sheets are conveyed in bundle form to a bookbinding processing stage (cover-binding location) situated in the mid-portion of the device, and from the tray the coversheets are conveyed separated into single sheets. To the upstream side of the coversheet binding stage, adhesive tape (or a hot-melt adhesive) is attached to the spine-portion endface of the inner-leaf sheets. In addition, the coversheet binding stage is fitted out with spine-folding press members. Conventional bookbinding units of this sort are known to suffer from the device requiring scaled-up installation space in that, for example, as disclosed in the cited reference, the inner-leaf sheets in bundle form are conveyed with a conveyor mechanism from a sheet supply unit to the bookbinding processing stage. Furthermore, when the three sides (the head, foot and fore-edge portions) of a sheet bundle in booklet form that has been book-forming processed in a bookbinding unit of this sort are trimmed true, the bookbinding unit is equipped with a trimming device that is distinct from the unit, and the trim-finishing is carried out in the trimming device.
Meanwhile, the present applicants have proposed, in Japanese Unexamined Pat. App. Pub. No. 2005-305822 and elsewhere, a unit that continuously bookbinding-processes image-bearing sheets from an image-forming unit. In the publication, a unit is proposed wherein sheets printed with images are collated and stacked in a bookbinding unit connected to a discharge outlet of an image-forming unit. These inner-leaf sheets are conveyed to an adhesive application position by a gripping conveyance means. There a spine portion of the sheet bundle is coated with adhesive. A coversheet is fed from a cover path that is different from the conveyance path for the inner-leaf sheets and set into place in a cover-binding location.
In both of the publications above, the unit collates and stacks simple sheets of the sheet bundle; the unit disclosed in Japanese Unexamined Pat. App. Pub. No. 2003-025759 is configured to set in a feed stacker a sheet bundle composed of simple sheets (a stack of single-leaf sheets). Likewise, the unit disclosed in Japanese Unexamined Pat. App. Pub. No. 2005-305822 collates simple sheets conveyed from the image-forming unit by stacking and storing them in a stacking tray.
The conventional bookbinding unit stacks simple sheets to compose the inner-leaf sheets of the sheet bundle, applies adhesive to the sheet bundle, then joins the sheet bundle to a central spine-binding portion of a coversheet. However, in print-forming inner-leaf sheets in a printing unit or like device, in some cases signatures are created by folding over a plurality of printed sheets. The plurality of sheets is stacked and folded over along the middle, the spine portion is stapled or saddle-stitched to create a signature, and presumably a plurality of signatures is stacked together to be encased in a coversheet as a booklet.
With conventional bookbinding approaches of this sort, prior to forming the text block into a book in the above-described bookbinding unit, it is known to subject the block to a milling process that cuts (grinds) it into a serrated form, and then to set the block into the inner-leaf tray. A problem with in this way finishing into booklets inner-leaf sheets in which sets of sheets have been folded over has been that if the sheets are milling-processed and the adhesive does not penetrate to the inside of the folded sheets, they cannot be securely bound together.